1. Field of the Invention
The present invention relates generally to a wireless flash photographing system and more particularly to a wireless flash photographing system in which light emission control of a slave flash apparatus, situated away from a camera, is effected by a flash light signal from a master flash apparatus provided in or on the camera.
2. Description of the Related Art
There is a conventional method of effectively using strobe light at the time of photographing, wherein a master flash and a slave flash, which is turned on by strobe light from the master flash, are used.
For example, Jap. Pat. Appln. KOKAI Publication No. 4-343343 (U.S. Pat. No. 5,384,611) discloses an example in which an identification signal of flash light is transmitted prior to moving a shutter front curtain. KOKAI No. 4-343343 also discloses that identification signals formed of a plurality of pulse beams are output from a flash apparatus built in or connected to a camera, and the identification signals are detected by a wireless flash not connected to the camera and received separately from other strobe light components.
In the technique of KOKAI 4-343343, however, the identification signal is output before the front curtain of the focal plane shutter is driven. In a camera system using this method, the identification signal needs to be output before moving the shutter front curtain. Thus, this method is not applicable to a camera which is not designed to output the signal before moving the shutter front curtain.
On the other hand, Jap. Pat. Appln. KOKAI Publication No. 61-45599 describes an example of "modeling light emission" using flash light, wherein an object is irradiated for a long time by making a light emission unit emit light intermittently. According to this example, even if a flash apparatus is not provided with a modeling lamp, shade can be confirmed in advance. Thus, the photographing is not failed.
In the meantime, it is possible to apply the technique of modeling light emission described in KOKAI No. 61-45599 to the wireless flash apparatus described in KOKAI No. 4-343343. In this case, however, the flash apparatus (hereinafter referred to as "master flash") built in or connected to the camera and the flash apparatus (hereinafter "slave flash") separated from the camera cannot be made to intermittently emit light at the same time. The reason for this is that if the light is intermittently emitted after the master flash has emitted a light emission start signal, the slave flash will stop light emission.
Even if the master flash and slave flash emit light simultaneously, the ratio of emission light in this case differs from that at the time of photographing. Consequently, the photographer fails to photograph an image which he had before the photographing. The reason for this is that the light emission method at the time of photographing is a so-called "successive light emission type light amount control method" in which the slave flash emits light first and then the master flash emits light, and the two flashes do not emit light simultaneously.
In addition, the applicant discloses in senior Japanese Patent Application No. 5-304423 a system wherein the light amount ratio, shade, etc. can be confirmed beforehand and the light emission can be controlled while maintaining a constant light amount ratio at the time of photographing upon receiving a proper light amount signal from the camera side or master flash side.
However, in the system of Patent Application No. 5-304423, the camera and master flash are connected by means of a connection cord. Thus, the design of this system is limited by the length of the connection cord.